1. Field of the Invention
The present invention relates to a toner transferring mechanism that transfers powdery toner using an agitating and transferring member having a blade portion formed in a spiral shape, the mechanism being adaptable for image forming apparatuses represented by copiers and printers. The present invention also relates to a developing apparatus and an image forming apparatus provided with such a toner transferring apparatus.
2. Description of Related Art
In electrophotographic image forming apparatuses such as copiers and printers, a photoconductive drum is widely used as an image carrying member. Generally, an image forming operation using a photoconductive drum is as follows: the surface of the photoconductive drum is uniformly charged at a predetermined potential by a charging apparatus, and that surface is then irradiated with light from an LED of an exposure apparatus, and the like whereby the potential is partially decreased owing to photo-induced discharge, and accordingly, an electrostatic latent image of an original document image is formed there. The electrostatic image thus formed is then developed by a developing apparatus so as to form a toner image. After the toner image is transferred to a sheet of paper, part of the toner left on the surface of the photoconductive drum is cleaned by a cleaning apparatus, and to prepare for the next image forming operation, the photoconductive drum is then irradiated with static-electricity eliminating light by a static-electricity eliminating apparatus, so that electrical charges carried by the photoconductive drum are removed therefrom.
Among other constituent components engaged in the above-described image forming operation, the developing apparatus is formed such that a housing thereof accommodates a predetermined amount of toner all the time. To achieve high-quality image forming, the toner so accommodated inside the housing needs to be evenly dispersed in a longitudinal direction of a developing roller inside the housing. Thus, in the developing apparatus, a toner transferring mechanism is widely employed that is provided with an agitating and transferring member having a blade portion thereof formed in a spiral shape on an outer circumferential portion of a rotatable shaft portion, and evenly dispersing the toner while transferring it in the longitudinal direction inside the housing with rotation of the member.
Moreover, in the cleaning apparatus, the toner removed from the photoconductive drum is temporarily accommodated, as waste toner, inside a housing of the cleaning apparatus. The waste toner, sequentially removed from the surface of the photoconductive drum and accommodated inside the housing of the cleaning apparatus during the image forming operation, needs to be discharged to outside, so that the housing is not filled with it. Thus, in the cleaning apparatus, as in the developing apparatus, a toner transferring mechanism is widely employed that is provided with an agitating and transferring member having a blade portion thereof formed in a spiral shape on an outer circumferential portion of a rotatable shaft portion, and transferring the toner to outside the housing with rotation of the member.
When the toner has been kept in the developing or cleaning apparatus for a long time, or when an ambient temperature of that apparatus rises, fluidity of the toner inside the housing decreases, possibly leading to that toner being stuck on the surface of the agitating and transferring member that agitates and simultaneously transfers the toner. When the toner is stuck on the agitating and transferring member and accumulated thereon, toner transfer performance is greatly degraded, possibly leading to a toner image, developed on the surface of the photoconductive drum, adversely affected thereby in the developing apparatus, and accordingly leading to a poor image formed on a sheet of paper. On the other hand, in the cleaning apparatus, such degraded performance possibly leads to waste toner overflowing and soiling the vicinity of the apparatus, or leads to waste toner adhering again to the surface of the photoconductive drum, causing degradation in cleaning performance. Moreover, the agitating and transferring member, as a result of being prevented from rotating smoothly by restriction imposed thereon, may be broken.
There have been some solutions proposed, with the aim of solving the above-described problems, for preventing toner from being stuck on a surface of an agitating and transferring member having a blade portion thereof formed in a spiral shape on an outer circumferential portion of a shaft portion; examples of such solutions can be seen in JP-A-H7-49637 and JP-A-2006-301604. Toner transferring mechanisms disclosed in these patent documents are each provided with a plurality of toner scraping members each making contact with a blade portion of an agitating and transferring member, the scraping members each swinging in accordance with rotation of the blade portion.
In the toner transferring mechanisms disclosed in the above-mentioned patent documents, the scraping members each formed with a sheet-like or wire-like member are made to rub a surface of the blade portion as the agitating and transferring member rotates; consequently, it is possible to prevent toner from being left on the blade portion and then stuck thereon, leading to improved toner transfer performance. In these toner transferring mechanisms, however, the plurality of scraping members are arranged at an interval which is equal to a spiral pitch of the blade portion of the agitating and transferring member; consequently, all the scraping members, when working together with the agitating and transferring member, form a same swinging pattern. That is, all the plurality of scraping members, as observed in a circumferential direction of the agitating and transferring member, make contact with the blade portion at same timing every time. Owing to this, the agitating and transferring member is more likely to receive a load, possibly leading to the agitating and transferring member interfered when rotating, or plastically deformed or bent to be broken.
Moreover, there is a concern that, in these toner transferring mechanisms disclosed in the above-mentioned patent documents, the scraping members are repeatedly deformed with rotation of the agitating and transferring member, and a load is intensively imposed on local part of the scraping members. As a result, there is a possibility that the scraping members are plastically deformed or bent to be broken at the part where the load has been intensively imposed. Moreover, there is a possibility that the scraping members thus broken interfere with the rotation of the agitating and transferring member, that the agitating and transferring member itself, an inner wall of a housing and other members inside the housing are broken, and that adherence of toner to the agitating and transferring member can no longer be prevented.